Ballasts, chokes and/or transformers serving as accessory elements for gas discharge lamps, typically fluorescent lamps, and having U-shaped core laminations and T-shaped magnetic return or magnetic circuit closing elements used with their transverse members between the outer members are known (Austrian Pat. No. 29 42 70). They have the advantage that with U-shaped core laminations surrounding the T-shaped magnetic circuit closing element, a mechanically stable structure is obtained, the parts of which can be secured at the abutting areas of the members, or legs, by interfitting engagement devices and/or can be pressed together with a bias; as a result, the required absence of hum can be assured by relatively simple means. The fundamental disadvantage of this U/T punch cutting of the core laminations is that a considerable amount of waste or scrap is produced during punching. Various methods have accordingly been proposed for producing such core laminations with less waste or scrap. In so doing, however, othermore or less important disadvantages have been imposed in return.
For instance, the T-shaped magnetic circuit closing element has been divided into two L-shaped lamina parts, which can be stamped out essentially without waste at the same time as the U-shaped core laminations (German Patent Disclosure DE-OS No. 26 38 780). This provision, however, necessitates handling three separate core elements in assembling the ballast, choke or transformer; this is labor-intensive and undesirable. Furthermore, the mechanical strength of the core as a whole is impaired.
These disadvantages are basically also found in a method (German Patent Disclosure DE-OS No. 27 45 701) in which the U-shaped core laminations are divided into two L-shaped lamina parts, and the T-shaped magnetic circuit closing elements for them are punched out in one piece. This method has still another disadvantage, which is that the L-shaped lamina parts and the T-shaped magnetic circuit closing elements must be punched out using different punches, which makes their manufacture more difficult. The same is basically true of yet another method (German Patent Disclosure No. 23 09 727), in which the disadvantage of a three-part core structure is overcome by producing M-shaped core laminations which are then bent into a U shape; here again, however, the T-shaped magnetic circuit closing elements must be stamped out using a separate tool.
Finally, still another method has been disclosed (British No. 1 328,160, to which French No. 20 70 783 corresponds), over which the present invention is an improvement. In this method, essentially waste-free punching of U-shaped core laminations and T-shaped magnetic circuit closing elements is possible using one tool. However, the T-shaped magnetic circuit closing elements are stamped out of the free spaces laterally defined by the outer legs of the U-shaped magnetic circuit closing elements in such a way that the outer legs of a U-shaped core lamination each laterally define one T-shaped magnetic circuit closing element located with its cross-leg between them. The long leg of this magnetic circuit closing element, in turn, is stamped out of the two outer legs--protruding between the outer legs of one U-shaped core lamination--of two other, opposed U-shaped core laminations; as a result, recesses are necessarily cut into these outer legs, corresponding to the middle leg of the T-shaped magnetic circuit closing element. This decreases the cross section of material on the outer legs of the U-shaped core laminations that is available for the magnetic flux. The width and the length of the middle legs of the T-shaped magnetic circuit closing elements are therefore limited. Also, it is not possible to provide recesses of approximately triangular cross section on the outer sides of the outer legs of the U-shaped core laminations, although such recesses are required for clamping on an approximately U-shaped clamping rail that assures the necessary bias at the sectional planes of the abutting core parts of the ballast, choke or transformer.